Hi miniegg,
I too went back full time last Jan when DS was 6 months old. I couldn't afford a nanny so opted for nursery which I was in torment over as so many reports on nurseries not being the best option for under 2s etc.
Anyway, it didn't take him long to adjust to the new routine and then to actually really enjoy it. For me, I settled back in immediately, despite being made to feel guilty by my stay at home mum friends.
It is hard, esp as I have a demanding job, work long hrs, do the majority of the housework, and have ds, but I feel like "me" again, which I didn't when I was at home (plus, like you, I couldn't afford not to work!). I think once you get over the guilt and realise that babies adapt easily to new situations, you just settle into a new routine, and you do survive!
(and, when ds had his 1st birthday party, I was so excited to see him mixing with all my friends' children, one of them actually said she wished she had as much patience with hers because being with them all day every day kind of wears you down) - anyway, that made me feel a lot less selfish for being a working mum!)
good luck!
x